Im blocking primer now and using 150 grit paper, and after i get done blocking, it seems to take a good bit of wet sanding with 500 grit to get the scratches out, and some are a little harder to get out. I spray 3 coats of primer on using the 4:1/2:1 (1/2 reducer for high build app.) I managed to get most out, but there are a few left here and there, but some times i start to go through the primer before i get them out. Can you go any finer than 180 and it still cut the primer down really flat? Let me hear the process of sanding ya'll go through before paint.